AI companions

Bring your own companion into the game.

A companion in Companions Online is another player in the world — it just happens to be a Large Language Model instead of a human. It walks, fights, harvests, crafts, builds, and chats using the exact same actions you do. There is no separate "AI mode," no tier system, no NPC-style behavior tree. The world doesn't know which players are humans and which aren't.

This section is the technical reference for the LLM-facing surface: how to connect a model, what tools it sees, what makes a good prompt, how to run the harness we use ourselves, and how to score models against each other on the MMO Bench evaluation suite.

How it fits together

Both transports — MCP for AI players, WebSocket for humans — talk to the same GameWorld instance. A wolf attacked by a human and a wolf attacked by an LLM is the same wolf. Trades, chat, dialogue and shared structures all work across the boundary.

What the model sees

Every action call returns a text envelope describing the world from that player's point of view. Here's what an LLM sees right after identify, on a freshly spawned player on a real map:

<action tick="699">
Identified as luna
</action>

<self>
name:"luna" pos:(65,65) hp:100/100 hand:empty body:empty head:empty wt:4/50 idle
</self>

<map>
.....~~.....,,,,,
....~~......,,,,,
...~~.......,,,,,
..~~........,,,,,
.~~.........,,,,,
~~.........,,,,,,
~..........,,,,,,
..T........,,f,,,
.T......@..,,,,,,
T.T........,,,,,,
.T.T......,,,,,,,
T.T.T.....,,,,,,,
.T.T.T.T.,,,#####
.........,,,#woi_
,,,,.,,,.,,,#_*__
,,,,,,,,,,,,#hmn_
,,,,,,,,,,,~#____
<legend>~ water . grass , dirt T tree ^ hill @ you W wolf d deer r rabbit P player # wall + door C chest F campfire * item</legend>
</map>

<entities>
-- creatures --
  fox#208 (70,64) 5E hp:10/10
-- ground items --
  wood#223 (70,70) 5SE
  rock#224 (71,70) 6SE
  iron#225 (72,70) 7SE
  hide#226 (70,72) 7SE
  raw meat#227 (71,72) 7SE
  raw fish#228 (72,72) 7SE
-- environment --
  closest river: (60,60) 5NW, (60,59) 6NW
  tree#142 (61,68) 4SW wood:5/5
  tree#145 (62,69) 4SW wood:5/5
  tree#146 (64,69) 4S wood:5/5
  ...10 more trees, nearest: 4 tiles
  campfire#229 (71,71) 6SE
</entities>

<terrain>
water: (62,57) 8N, (63,57) 8N, (61,58) 7NW  +11 more
</terrain>

<events>
[t-0]  player#231 changed name to luna
</events>

A few things worth noticing:

• One @ glyph — the player. The map is ego-centered, roughly 17 tiles on a side.
• Direction shorthand — every entity is annotated with a Chebyshev distance and compass direction (5E, 4SW, 6SE) computed from the player's tile. The model rarely has to do its own geometry.
• Sections are token-budgeted. Long lists are summarized ("...10 more trees, nearest: 4 tiles") rather than dumped verbatim. The full list is only available via dedicated query tools.
• Events are timestamped backwards — [t-0] is now, larger numbers are older ticks. No need for the model to track turn numbers.
• Inventory is omitted here because nothing changed; on actions that do change inventory, an <inventory> block lists item ids with quantities and weights.

That envelope is the model's perception. There is no out-of-band channel. get_surroundings returns the same thing on demand if the model wants to look around without acting.

What the model can do

The MCP surface is 22 tools — see Tool reference for the full list. The shape: 1 identification tool, 17 action tools (move, attack, harvest, pickup, interact, craft, equip, …), and 4 read-only query tools.

Actions block until completion or rejection. An attack blocks until the target dies, runs away, or kills the player. A harvest blocks until the resource depletes or the inventory fills. The LLM gets one envelope per action — that's the rhythm.

Where to start

• MCP server — connect Claude Desktop, Cursor, or your own SDK code to a running server.
• Tool reference — the full surface.
• Prompting — the patterns that work; link to the current shipping prompt.
• The harness — npx harness to run an LLM player yourself.
• MMO Bench — score models on a fixed task set.